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EASY EXPEKIMENTS 



IN 



PHYSICAL SCIENCE, 



FOR 



ORAL INSTRUCTION IN COMMON SCHOOLS, 



BY 



LE ROY C. COOLEY, Ph. D., 



PROFESSOR OF NATURAL SCIENCE LN THE NEW YORK STATE NORMAL SCHOOL. 









NEW YORK: 
CHARLES SCR1BNER AND COMPANY. 



Qc 3 3 



Entered according to Act of Congress, in the year 1870, 

By LE ROY C. COOLEY. 
In the Office of the Librarian of Congress at Washington. 



PREFACE. 



It is coming to be very generally believed by educators 
that one of the most important aims of primary instruc- 
tion should be to discipline the child to habits of quick 
and accurate observation, and to the power of making sim- 
ple but correct inferences from the facts which his senses 
reveal. Surely this result can be reached more easily by 
means of those facts which nature communicates through 
the senses than by subjects which have no natural depend- 
ence upon material forms ; and hence the superior adap- 
tation of the simple facts of physical science to the wants 
of common-school instruction. 

But the only way to strengthen mind is to make it 
work. If the senses are to be developed and disciplined, 
the child must be allowed, and, if need be, compelled, to 
use his senses for himself. The teacher is to guide him, 
but not to carry him. His mind is to be directed toward 
material things, and taught to see their forms and charac- 
ters as they themselves present them. The instructor is 
to be his guide, but Nature is herself to be his teacher. 
The intelligent teachers of common-schools are eagerly 
asking how can this theory be wrought into practice. 
Lack of time and lack of material seem to almost forbid 



iv PREFACE. 

the attempt : lack of time, because custom and public 
opinion demand so much knowledge of books in all the 
branches which overcrowd the primary course ; and lack 
of material, because apparatus other than a blackboard 
and a few maps is, in most common-schools, a thing un- 
heard of. It is pleasant to anticipate a time when the 
higher and theoretical parts of arithmetic and grammar 
shall be reserved for the high-school course of study, and 
their places in the common-school left to the more appro- 
priate study of nature. It is pleasant to anticipate the time 
when every common-school shall be provided with an ap- 
propriate set of apparatus, through which Nature may teach 
her simple truths to children in her ewn playful and child- 
like manner. The time is doubtless coming when both 
these anticipations will be realized, and all the quicker 
will it come if teachers will only begin the work by using 
the very little time and means already at their disposal. 
Some have already begun : they find it possible to secure 
time for a short exercise each day, or at least two or three 
times a- week, in which they perform simple experiments 
with such objects and utensils as they find at hand, much 
to the delight and profit of their schools. Letters from 
several of these announce their surprise at the interest 
thus aroused, not only among pupils, but among parents 
also. "Whole neighborhoods are in some instances awak- 
ened, and it will not be difficult in such cases to obtain 
money for the purchase of better means of illustration ! 
Now this little book is offered as an aid to the teachers 



PREFACE. v 

who are, or who desire to be, engaged in this work. It 
is made up of experiments of the simplest kind, which, 
with few exceptions, can be performed with such appa- 
ratus as can be collected anywhere almost without expense. 
These experiments are arranged in groups, each group 
teaching some elementary fact or principle of science. 
They are selected from among those which the writer has 
long been using in the earliest stages of his instructions 
to his classes, and which are now being reproduced by 
young teachers who have gone out into the public-schools 
of the State, and from whom reports of abundant success 
are received. There is, therefore, good reason to believe 
that they are practical and instructive. 

But there is another purpose which this little book is 
designed to serve. The best teachers of natural science 
are unanimously of the opinion that the very best results 
can be secured only by allowing the student to make 
experiments for himself. In the study of science in high- 
schools and academies, good text-books are very desirable ; 
a full course of illustrative experiments by the teacher is 
indispensable ; but if, added to these, there can be a course 
of simpler experiment by the pupils themselves, the value 
of both will be enhanced. 

Now the experiments described in the following pages 
are such as intelligent boys and girls can make with little 
or no assistance. All that the teacher need to give them 
is encouragement, and it is believed that he would find 



v i PREFACE. 

his own work more productive if, in addition to the text- 
book and his lectures, this course of simple experiments 
could be put into the hands of every pupil in his class. 
Students can not too early begin to acquire the habit and 
the power of verifying the statements in the science which 
they study. This they can do in an elementary course of 
study by experiments of the simplest character made with 
apparatus the most inexpensive. 



APPARATUS. 



The following list comprises the most important pieces 
of apparatus needed for the performance of the experi- 
ments described in this book. The articles named in the 
second column may be obtained very cheaply of apparatus 
dealers : those in the first can be found at home in any 
district. A great many other things will be used, but 
they are too common to need even to be named here. 

Fruit-cans. Glass tubing — \ lb. ass'd sizes. 

Ale-glasses. Eubber tubing — 2 ft. 

Bottles. Alcohol lamp. 

Corks. Flask — glass, 1 pt. 

Plates. Test tubes — J doz. 6 inch. 

File. Convex lens. 

Funnel. Violin string. 

Tuning-fork. Glass tube — for frictional elec. 

Shot. Sealing-wax. 

Besides this apparatus some chemicals are necessary. 
All these, except some which are too common to need 
mentioning, are comprised in the following list. They 
may also be obtained of the apparatus dealers at very 



trifling expense. 




Alcohol. 


Sulphuric acid. 


Cochineal. 


Hydrochloric acid 


Litmus. 


Nitric acid. 


Sulphur. 


Ammonia. 




Copper clippings. 



EAST EXPEKIMENTS 



IN 



NATURAL PHILOSOPHY. 



"Always bear in mind that the simplest experiments, or those most 
easily imitated by the pupils, are the best." — Nature, 



INTEODTJOTIOK". 



Divisibility. Ex. 1.— Take a glass jar, holding lialf a 
gallon, — a fruit-can answers the purpose well, — and fill it 
with water. Next take a little powdered cochineal, as 
much as will lie upon the end of a penknife-blade, which 
will not be more than half a grain by weight, and dissolve 
it in a thimbleful of water. Finally pour the cochineal 
into the clear water in the jar. Notice the cloud-like 
masses of colored water slowly making their way down- 
ward. After a little time stir the water briskly, and then 
see that every part of it is distinctly colored. 

Now it is said that there are as many as 30,000 drops 
of water in a half-gallon, and that it must take as many 
as 100 little particles of the cochineal to color a single 
drop distinctly. 

In this experiment, then, a single half-grain weight of 
cochineal has been divided into not less than 3,000,000 
pieces. 

Ex. 2.— Place a goblet on the table and fill it about 
one half full of water. Take a piece of loaf-sugar as large 
as a walnut, and by blows break it into small pieces. 
Put these pieces into the water and stir them about vig- 
orously. After a little time notice that the sugar has 
entirely disappeared. 

In this case the body has been divided into pieces so 
small that, being colorless, they can not be seen at all. 



12 INTRODUCTION. 

J^». 3.— Take a small piece of marble, and by pounding 
it reduce it to the finest powder : the separate grains are 
almost invisible, and yet each one of them is a piece of 
the original block. 

We learn from these experiments that some bodies can 
be separated into many parts. And when we think of 
others which we have not just now tried, we remember 
that they too can be broken or cut into pieces. Now this 
quality of matter, by virtue of which bodies may be sepa- 
rated into pieces, is called divisibility. 

Remakks. — Teachers will notice that the descriptions 
of the foregoing experiments are minute and clear enough 
to forbid any failure in the performance of them. But 
these descriptions only show the work which teachers 
must do ; they do not give the language which they must 
use. While making an experiment the teacher ought, by 
skillful questions and appropriate remarks, to keep the 
attention of the children upon it, so that every part of the 
apparatus shall be observed and every action definitely 
seen. Above all things ought care to be taken that the 
final inference is seen to be the natural consequence of the 
facts observed in the experiments. The tendency will 
doubtless be for the teacher to do all the talking, while 
the pupils rest contented with simply repeating what they 
hear. This should be avoided. 

The pupils should themselves be made to describe the 
apparatus while they look at it ; to announce the results 
as they occur ; and to interpret them as fully as possible 
and with as little assistance as may be practicable. 

No two intelligent teachers will ever work by exactly 
the same method, but yet the principle just stated ought 
to be the foundation of every plan and determine the 



INTRODUCTION. 13 

detail of every attempt to teach science, in its most ele- 
mentary form, for which these experiments are designed. 
The following conversation occurred between a teacher 
and his class in regard to the experiments just described. 
It will serve to illustrate the method of making the pupil 
use his senses to acquire knowledge. 

Teacher. — I have here three substances about which 
we want to learn something to-day. One of them— this 
which you see (holding it up in view of the class) — is 
cochineal; another (showing it) is a lump of loaf-sugar; 
and the third (showing it also) is a piece of marble. I 
want to show you some things that can be done with 
these, and I would like to have you to tell me exactly 
what you see and learn. 

1st Expemment.—Now notice (teacher takes a half- 
gallon jar and fills it with water) : what have we here ? 

Pupils. — A jar of water. 

Teacher. — I must tell you now that the jar holds one 
half a gallon; and now think a moment, whether you 
have not often seen water that looked very unlike this. 
Tell me, then, what you see before you. 

A few Pupils. — A half-gallon of clear water in a jar. 

Teacher. — Yes ; you all can see that the water is not 
muddy nor colored ; it is clear, and you know I told you 
that the jar holds half a gallon. 

Now here (dipping up a little cochineal upon his knife- 
blade) is the cochineal. It was not always as you see it 
now. It was found in the shape of little balls about as 
large as large shot, each covered with a grayish coating ; 
but now what do you say of it? 

Pupils. — A reddish powder. 

Teacher. — The little balls have been broken into pieces 



14 INTRODUCTION. 

— indeed, crushed into this fine powder. But see what I 
will do with it. Just the little on my knife — there is not 
more than the weight of half a grain — remember this, 
I will use in this way (putting a little water into a 
goblet and the powder into it, and thoroughly stirring 
them together). Now, John, come and look at this, and 
tell your mates whether you can see the powder. 

John. — There is a little at the bottom. 

Teacher. — Just a little ; but where is all the rest? 

John. — It looks like red water. 

Teacher. — Yes; you do not see the powder in the 
water, but the water looks red because the little particles 
of powder are broken up into such very little pieces that 
John could not see them, and these little pieces are scat- 
tered throughout every part of the water. 

But now look again (pouring the "red water" into the 
jar) : who will tell me what is going on now ? 

Several Pupils. — The cochineal is going to the bot- 
tom ! 

Others. — It is mixing with the water ! 

Teacher. — When we have watched these very pretty 
cloud-like streams of colored water long enough, I will 
stir the water thoroughly in the jar (doing so after a 
pause). Now tell me if you see any change made in the 
water. 

Pupils. — It is red now, all through ! 

Teacher. — But you know there was a whole half- 
gallon of water and only half a grain of cochineal ! 
Now let us see, — how many drops of water do you sup- 
pose there are in the jar ? Of course you do not know, 
and I will tell you that it is said that there are not less 
than 30,000. It is thought, too, that it would need as 
many, at least, as 100 little pieces of cochineal to color a 



INTRODUCTION. 15 

single drop, perfectly in every part of it. And yet the 
half-grain has colored the half-gallon ! 

Now who will answer quickly, — If it take 100 pieces 
of cochineal to color one drop of water, how many pieces 
will it take to color 30,000 drops ? 

Pupils. — One hundred times 30,000 are — (after hesita- 
tion a few answer correctly) 3,000,000. 

Teacher. — That is right. Now look again at this 
water: it is crimson-colored, — every drop of it. Into 
how many pieces does this experiment show the half- 
grain of cochineal to be divided ? 

Many Pupils.— Into 3,000,000 pieces ! 

Teacher. — Surely it was a very little thing to be broken 
up into such a multitude of pieces ! But now for the 

2d Experiment. — Let us use this little lump of sugar. 
What have we here? (Placing a goblet on the table and 
half filling it w r ith water). 

Pupils. — A goblet of water. 

Teacher. — Now watch the sugar (dropping it into the 
water and stirring it about a little time). Well, what has 
happened ? 

Pupils. — It has fallen to pieces. 

Teacher. — I will continue stirring these pieces about in 
the water (doing so until the sugar is dissolved) ; and now 
can you see them ? Come and look. (To those who came) 
Well, where is the sugar ? 

Pupils. — It is in the water. 

Teacher. — But can you see it ? 

Pupils. — No. 

Teacher. — How then do you know that it is in the 
water ? 

Pupils. — We saw you put it in there. 

Teacher. — Yery good : you saw it put there, and it has 



16 INTRODUCTION. 

not been taken out again. But you did see it in the water 
at first : why can you not see it now? 

Pupils. — Because it is broken up and all scattered 
through the water. 

Teacher. — That is it exactly ! And now you can tell 
rue what this experiment shows us about sugar, can you 
not? 

Pupils. — That sugar can be. broken up into very little 
pieces. 

Teacher. — Yes; or you might say, — it shows us that 
sugar can be divided into pieces which are so small that 
they can not be seen. 

Now let us see about the marble. 

3d Experiment. — George, now I place the marble upon 
this brick which I have brought here on purpose; won't 
you come and strike it with this hammer ? (He does so.) 
There, what have you done to the marble? 

George. — I have broken it. 

Teacher. — Now take one of the pieces and strike it. 
(He does so.) There, what have you done to the piece ? 

George. — Crumbled it all to powder. 

Teacher. — But not to very fine powder ; but now sup- 
pose you strike these little pieces, will they be broken 
again ? Try it, George. (He does so.) Well ? 

George. — The powder is fine now. 

Teacher. — Then you must have broken the little pieces 
up into still smaller ones. We can hardly see them sepa- 
rately. And now, scholars, tell me what all this shows 
about marble. 

Pupils. — That marble may be divided into little pieces. 

Teacher. — Yery good. We have now tried three 
things,- — cochineal, sugar, and marble. We have found 
that each may be divided into very little parts. They 



INTRODUCTION. 17 

"are alike in this respect, even though so very different in 
most others. This quality of these bodies, which allows 
them to be broken or separated into parts, is called 
divisibility. Can you think of other substances which 
can be divided ? (Several things are quickly mentioned.) 
All these things have the same quality as you have seen 
the cochineal, the sugar, and the marble, to possess. What 
is that quality called ? 

Pupils. — Divisibility. 

Teacher. — What, then, does this word, — divisibility, — 
mean ? I will write its meaning on the blackboard for 
you. 

" Divisibility is that quality of bodies which allows 
them to be cut or broken into parts." 

Perhaps no other teacher would do just exactly as this 
one did, in conducting this exercise, but in some respects 
his example is worthy of careful imitation. 

1st. He evidently had a definite plan marked out 
beforehand. No teacher should attempt a single experi- 
ment until he has tried it, studied it, and formed his plan 
for using it. 

• 2d. His object seemed to be to make the pupils see 
clearly what occurred, and to infer correctly from what 
they saw. Let every teacher lay every plan and work out 
every detail with direct reference to these two results. 

3d. Hence he called upon his pupils to tell him what 
things were being used and what effects produced, instead 
of describing them himself. So should every teacher do, 
telling the pupils only those things which the apparatus 
does not clearly show. 

It will be found to be an excellent plan, especially after 



18 INTRODUCTION. 

pupils have had some experience in these exercises, to 
first, put before them all the apparatus for an experiment 
ready for use and ask some one pupil to describe it fully, 
then to make the experiment deliberately and* silently, 
afterward calling upon a second pupil to tell you what 
you did, and upon a third to tell you what changes or 
effects he saw produced, and upon a fourth to tell you 
what he thinks the experiment teaches. Repeat the ex- 
periment, if need be, to bring out any essential point 
which the pupils did not at first discover. 

It will also be well to encourage the pupils to make ex- 
periments for themselves. Call upon individuals to help 
you at times. Especially if, during an exercise, one is seen 
to be inattentive, nothing can be better than to ask him 
to help you in the experiment being made. Let him do 
some part of it which you know he can do well, and take 
care that he do not fail. His success will do more than 
any thing else can to secure his attention in the future. 

^ The following experiments furnish abundant material 
for such exercises as have just been indicated. If used at 
all in common-schools, they can not fail to awaken lively 
interest among the scholars, and will always leave their 
minds in better condition to pursue their regular studies 
to better advantage. If used skillfully by the methods 
just pointed out, their own educational value will not be 
surpassed by that of any other branch of study. 



THE PEOPEETIES OF MATTER 



Impenetrability. Experiment 4. — A glass jar may 

be partly filled with water (Fig. 1). Let a block of wood 

* c — ^ of convenient size and shape be then pushed 

>, down into the water. Notice that as the 

wood enters, the liquid rises in the jar, and 

that it falls again when the wood is taken 

out. We see that these two bodies, wood and 

water, can not be put into the same place at 

the same time. 

Ex. 5. — Let an inverted goblet be held 
Flg * lm with its mouth on the surface of the water 
in the jar. Notice that the goblet is full of air. Next, 
push the goblet down into the water. Notice that the 
goblet is still full of air, the water not rising into 
it. We see, here, that water and air can not be 
put into the same place at the same time. 

Ex. 6. — Hold the inverted goblet in the water 
as before, its mouth being an inch or more under 
the surface. Having a large cork, fixed upon 
the end of a bent wire (Fig. 2) for a handle, push 
it down under the edge of the goblet and then 
up into the air within. Notice that as the cork Elg * 2 " 
goes up into the air some air-bubbles escape through 
the water. We see that air and cork can not be put into 
the same place at the same time. 




20 PHYSICAL SCIENCE. 

What is seen in these experiments is true of all bodies ; 
no two can be put into the same place at the same time. 
This property of matter, by which no two bodies can 
occupy the same space at once, is called impenetrability. 

Indestructibility. Ex. 7. — Into a small tin cup put 
a little fine sugar and carefully weigh them. (See Ex. 32, 
Fig. 7.) Add water enough, afterward, to dissolve the 
sugar. Notice that the sugar has all disappeared. Next 
place the cup over a stove or a lamp-flame, and continue 
the heat until the water is driven away and the cup and 
its contents are thoroughly dry, taking care that nothing 
is lost by boiling or flying over. Notice that the sugar is 
to be seen in the cup again. Finally weigh the cup and 
its sugar ; the weight should be the same as before the 
sugar was dissolved. We see that sugar may disappear 
without being destroyed. 

Whenever any substance disappears from any cause, its 
form is changed, but the substance is never destroyed. 
This property of matter, by virtue of which it can not be 
destroyed, is called indestructibility. 

Elasticity. Ex. 8. — Take a piece of steel wire and 
hold one end firmly in one hand. With the other hand 
take hold of the other end and pull it over to one side. 
Notice that the wire yields to the force of the hand. 
Next, let go the end which has been pulled away, and 
notice that it springs back to its former place. We see 
that this wire w T ill yield to a force and spring back again 
when the force is taken aw^ay. 

Ex. 9. — Having a glass ball — an " agate" used by 
boys in playing " marbles" — drop it upon a stone or other 
hard surface. Notice that it bounds upward to consider- 



PROPERTIES OF MATTER. 21 

able height. Now the ball bounds because it is, for the 
moment, flattened a little just where it strikes the stone, 
but at the next instant it springs back to its former shape, 
and this springing back throws the ball upward. This 
being so, we see that even glass will yield to a force and 
afterward spring back. 

This property of bodies, shown by the wire and the 
glass, by which they spring back to their former position 
or shape after having yielded to some force, is called 
elasticity. # All bodies are more or less elastic. 

Ductility. Ex, 10. — Hold the middle of a small glass 
tube in the flame of an alcohol lamp until about an inch 
of its length is made red-hot. It will be necessary to roll 
the tube over in the flame constantly to heat it on all sides 
alike. When heated to redness, take it from the flame, 
and at the same time pull with both hands lengthwise of 
the tube. Notice that the glass is drawn out into a long 
and thread-like wire. 

Many substances, like glass, may be drawn out into 
w^ire. Metallic wires are very common. The property 
of matter by which a body can be drawn into wire is 
called ductility. 

Ex. 11. — Taking hold of the ends of the glass still 
attached to the wire, use them as handles, and on moving 
them about, notice how flexible flne threads of glass are. 

Ex. 12. — Break one handle off, leaving the fine wire 
still attached to the other. Put the fine end down deep 
into a vessel of water and the other end in the mouth. 
Blow strongly, and notice the bubbles of air coming in a 
steady stream up through the w T ater, showing that the fine 
thread is still a glass tube. It can not be drawn so fine as 
not to be a tube. 



22 PHYSICAL SCIENCE. 

Combustibility. Ex. 13. — Take as much potassic 
chlorate as may lie upon a penny and mix it with an 
equal quantity of sugar. Put this mixture upon a piece 
of card-board resting on the top of a goblet. Add next 
two or three drops of strong sulphuric acid, and quickly 
take the hand away from over the mixture. Notice 
that a violent and surprising combustion immediately 
follows. 

Wood, coal, oil, and many other bodies burn freely. 
This property of matter, by which it is able to burn, is 
called combustibility. 

Explosibility. Ex. 14. — Let as much potassic chlo- 
rate as may lie on the point of a penknife-blade be put 
into a mortar with the same quantity of sulphur. Larger 
quantities can not be safely handled. Next rub the mix- 
ture with the pestle. Notice a sharp report or perhaps 
several reports in succession if the rubbing be continued. 

Gunpowder will explode when touched with a burning 
match, and some other substances have the same property. 
This property of substances, by which they may be made 
to explode, is called explosibility. 



ATTRACTION. 



Gravitation. Ex. 15. — Let a ball be dropped from 
the hand. Its falling toward the earth is an example of 
what is seen perhaps every day of our lives. All bodies 
fall toward the earth. 

But not only is this true ; the astronomer finds also that 
all the heavenly bodies are pulling each other toward 
themselves. Indeed, all bodies tend to approach each 
other. The attraction which pulls them toward each 
other is called gravitation. 

Cohesion. Ex, 16, — Take a half-sheet of letter-paper 
and gum each end to a smooth bar of wood longer than 
the width of the paper, so that each end will project be- 
yond the edge. (Fig. 3.) Let the bars 
be exactly parallel. Now with the pro- 
jecting bars as handles, two persons 
may try to pull the paper apart. An 
astonishing force will be needed to do it 
when the pull is steady and square. 
Notice that the parts of the paper are 
held together very firmly. We see that 
there is an attraction among its parts. 

Ex. 17. — An apple being cut into two halves, let their 
fresh surfaces be pressed together again, and notice how 
hard it is to pull them apart again afterward. We see 
that there is attraction between them. 




24 PHYSICAL SCIENCE. 

Ex. 18. — Let two oullets be flattened and then smoothed 
on one side of each with a knife until they will fit each 
other closely. Next press the two freshly-cut surfaces 
firmly together, and afterward let them be pulled apart 
again. Notice that it needs considerable force to pull 
them apart. 

In all these experiments we notice an attraction between 
parts of one body or of two bodies of the same kind of 
matter. Now the attraction which holds the parts of a 
body or of different bodies of the same kind together is 
called cohesion. 

Adhesion. Ex. 19.: — Having two test-tubes, or even 
two small cups, put some oil into one and some mercury 
into the other. Into the oil plunge a rod of wood and 
into the mercury another. Now taking the wood from 
the oil, we notice it covered with a film of that substance. 
Next take the wood from the mercury, and notice not a 
drop of the liquid upon it. We learn that there is an at- 
traction between wood and oil, while none is shown be- 
tween wood and mercury. 

Ex. 20. — Have two cups of water : into one of them 
plunge a rod of wood, into the other a piece of wax, or 
even a candle. On taking them out, notice that water 
clings to the wood, and wets it, but not to the wax or 
candle. We learn that there is an attraction between 
wood and water, but apparently none or very little be- 
tween wax and water. 

Ex. 21. — Draw a crayon along the surface of the black- 
board, and notice its particles clinging thereto. 

We learn from these experiments that there is, in some 
cases, an attraction between different kinds of matter 
which holds their particles together. This attraction, 



ATTRACTION. 25 

which holds particles of different kinds together, is called 
adhesion. In some cases it is called capillary force. 

Capillary Force. Ex. 22. — Let some water be 
colored with ink, or, far better, with cochineal. Take a 
small glass tube — its diameter not more than ^ of an 
inch — and put one end of it into the colored liquid. 
Notice the liquid springing up into the tube quickly 
and remaining there much higher than it is outside. 

Ex. 23. — Stand a piece of flat glass in the w T ater, and 
notice the liquid rising a little way up along its sides. 

Now the attraction, shown in these experiments, by 
which a liquid is lifted in small tubes or along the sides 
of solid bodies, is called capillary force. 

Ex. 24. — Wrap a common bottle in a strip of blotting- 
paper which is as wide as the bottle is high, and fasten its 
edges with wax. Next fill the bottle with water made 
black by ink. Finally, stand the bottle, thus prepared, 
on a common dinner-plate, and pour water upon the plate 
to come in contact with the lower edge of the paper on 
the bottle. Notice that the water will be soon seen slowly 
rising up the paper, and in a little time it will have 
climbed to the top of the bottle. 

Remember, also, that oil rises in a lamp-wick in the 
same way ; that water will wet a piece of cloth through- 
out in a little time, if only one corner touches the liquid ; 
that ink spreads on blotting-paper, and other similar and 
familiar facts. In all these cases, as in the experiment, 
capillary force is causing a liquid to penetrate porous 
solids. 

Ex. 25. — Having two strips of glass — three inches 
long by an inch in width is a convenient size — put a nar- 
row piece of card-board between their ends, and then 

2 



26 



PHYSICAL SCIENCE. 



cement them together with a little sealing-wax. The two 
plates are then parallel and very near together — separated 
only by the thickness of the card-board. Take the sealed 
end in the hand and bring the other end of the plates 
down into some colored water. Notice the fluid instantly 
leaping up to some height, where it remains between the 
plates. 

Ex. 26. — Cement two other similar plates of glass so 
that they shall not be parallel — one edge of the pair 
being in contact, the other edges being separated perhaps 
an eighth of an inch. Put the lower end of this pair of 
plates into the colored water; it will spring up quickly 
as before. But notice that its surface is in the form 
of a beautiful curve (Fig. 4), and larther, that the liquid 
is lifted highest where the plates are nearest 
together. 

Ex. 27. — Select two small glass tubes, 
one of which shall have a diameter twice 
as great as the other. Put one end of each 
into the colored water and it will rise in 
both. Notice that the fluid rises highest 
in the smallest tube— /w^ twice as high 
if one tube is exactly one-half diameter 
of the other. (See Coolers Philosophy^) 




Fig. 4. 



WATER. 



Mobility. Ex. 28.— Fill three goblets, one with small 
marbles or large peas, another with fine shot, and a third 
with water. Invert a dinner-plate as a cover over each. 
By holding the plate tightly pressed upon the mouth of 
the goblet with one hand, while the goblet itself is grasped 
by the other, both may be turned over together without 
spilling the contents of the glass. Do this with each in 
turn, and the three goblets will be left standing, full, 
but bottom upward, on the plates. Next carefully lift the 
goblet containing the marbles, and notice how they spread 
out upon the plate, and see that they do so because they 
are such smooth balls, without force to hold them together. 
Then lift the goblet containing shot, and notice that they 
roll out upon the plate in tbe same way and for the same 
reason. Finally lift the goblet containing water, and 
notice it, also, spread itself out upon the plate just as the 
others did. We may give the same reason : water consists 
of little ?, very little smooth halls, without force enough 
among them to hold them together. 

Because water consists of such very small and smooth 
bodies, it is able to move about so freely as it does. They 
roll over and around each other with the greatest ease. 
This freedom of motion among its molecules is called 
mobility. (See Cooley's Phil., p. 38.) 

Pressure. Ex. 29. — Having a lamp-chimney, whose 
lower end is smooth and even, cut a circle of tin large 



28 



PHYSICAL SCIENCE. 





Cr^ 



Fig. 5. 



enough to cover it. Make a small hole in the center of 
the disk and pass a string through it, letting a knot in the 
lower end prevent the string from coming out. 
Now run the string through the lamp-chimney, 
ft «fl> " ari( i by means of it hold the tin up tightly 
^ II a against the end of the glass until it is pushed 
down to the middle of a jar of water. Then 
let go the string (Fig. 5), and notice that the 
tin — a heavy metal — does not sink. Notice 
also that there is nothing but water to hold it 
up. The experiment teaches that water exerts 
an upward pressure. 

Ex. 30. — Take a glass tube, bent in two 
places at right-angles,* and hold the finger 
tightly over one end, or close it with a cork. Let some 
water, colored with ink or cochineal, be poured in to the 
other end ; it will fill that arm of the tube and a part of 
the horizontal portion. (Fig. 6.) g 
Now let the air slowly pass from 
under the finger or the cork at 
the closed end, and notice the 
water moving downward in one 
arm, sideways through the hori- 
zontal part, and upward in the 
other arm of the tube. By this 
motion of the water we learn that it is exerting pressure 
downward, sidewise, and upward, at the same time. 



Z 



Fisr. 



Ex. 31. — Place a small block of wood upon the surface 

* A glass tube held in the flame of an alcohol lamp until it begins to 
soften may be easily bent into any required shape. Roll it in the flame to 
heat all sides alike, and when it begins to yield, press it gently into the 
desired shape. 



WATER. 29 

of water in a jar, and by means of a rod of wood or iron 
try to push it down to the bottom. Notice its struggles 
to stay at the top, and also that there is nothing but 
water to push it up. 

Ex. 32, — To the middle point of a bar of wood let a 
cord be tied so that the bar 
will balance when the string 
is held in the hand. This 
bar is a very good scale-beam. 
From one end hang a stone 
about the size of a hen's egg, 
and from the other end hang 
a small cup, into which put 
just sand enough to make it 
balance the stone. (Fig. 7.) ^s 
Now let the stone be made Fi s- 7 - 

to hang down into a vessel of water. Notice that it is no 
longer balanced by the cup of sand : it is lighter in the 
water than out of it. See that it must be the water that 
helps to hold it up. 

From these two experiments we learn that water presses 
upward against bodies immersed in it. 

Ex. 33. — Fill a pitcher brimful of water. Place a 
dish under the lip to catch the water soon to run over, 
and smear the under side of the edge of the lip with tal- 
low to prevent water from running down the side of the 
pitcher. Lay the block of wood (Ex. 31) carefully upon 
the surface, and notice that water runs over the lip. After- 
ward notice that the upward pressure of water just sus- 
tains the wood, and hence must just equal the weight of 
the block. Hang a cup from each end of the scale-beam ; 
make them just balance. Now dry the wood and put it 
into one cup; take the water that was pushed over the 



30 PHYSICAL SCIENCE. 

lip of the pitcher by it and put it into the other cup. 
Let all this work be very carefully done. Then notice 
that the wood and water just balance. We thus learn 
that the water displaced by a body which floats, weighs 
just as much as the body itself. 

Ex. 34. — Empty the w r ater from the cup and make the 
two cups balance each other again. Then tie the stone 
(Ex. 32) to one end of the u scale-beam " by a string 
long enough to let it hang down below the cup, and 
put sand into the other cup to balance it. Next let the 
stone hang into the pitcher fitll of water and catch the 
liquid displaced. Notice that the stone is lighter now 
than before. How much lighter ? Another experiment 
will tell. 

Ex. 35, — Put the water that was displaced by the stone 
into the cup above it, and notice that the balance is re- 
stored, and learn that the weight which this heavy body 
loses in water is just equal to the weight of water it dis- 
places. 



AIR. 



Compressibility. Ex. 36. — Take a glass tube sev- 
eral inches long and pass one end of it tightly through 
a cork which has been selected to fit the neck of a 
vial. Push the cork end of this tube into some colored 
water and close the other end with the finger. Keeping 
the end closed, lift the cork from the water, and press 
it tightly into the neck of the vial, at the same time 
taking the finger from the end of the tube. Notice now 
that the colored water stands some distance up the tube 
— the space below being filled with air. 
(Fig. 8.) 

Next slip the end of a piece of rubber 
tubing over the end of the glass tube. 
Apply the lips to the end of this and gently 
press the breath into it. Notice that the 
water in the tube moves toward the vial. 
But there is no escape for the air, and hence A 
it must be crowded into smaller space than 
it occupied before. We thus learn that air 
is compressible. Fig< 8> 

Expansibility. Ex. 37.— Now apply the lips to the 
rubber tube again and draw the air out of it. Notice the 
colored water moving away from the vial, and see that 
the air now fills more space than before. We thus learn 
that air is expansible. 




32 



PHYSICAL SCIENCE. 



Elasticity. Ex. 38. — Using the same apparatus, let 
the breath be alternately pressed gently into the tube and 
then withdrawn, and notice the water alternately moving 
back and forth in the tube. The air first yields to the 
force of the breath ; it then springs back when the force 
is withdrawn. We see that it is elastic. 



Pressure. Ex. 39. — Place one end of a straight glass 
tube in colored water, and with the lips at the other end 
withdraw the air. The colored water is seen rising in the 
tube. It is pushed up, but notice that there is nothing to 
push it up but the air that rests upon the surface of the 
water in the vessel. 

Ex. 40. — Push a glass jar (a fruit-can) down into a pail 
of water until it is filled. Take hold of the bottom of the 
jar and lift it until only the edge of the mouth of it is 
under the water in the pail. Notice that the jar is still 
full of water. Something holds the water up ; there is 
nothing to do it but air outside. 

If a shelf is fastened in one side of the pail just under 
the surface of the water, as may be very 
easily done, the full jar may be left mouth 
downward on the shelf; the water will 
not run out. 

Ex, 41. — Fit a long-necked bottle with 
a cork through which two tubes pass. 
Both tubes should reach some distance 
into the bottle. One should reach some 
inches outside, the other must be shorter. 
To the shorter one the end of a rubber 
tube must be attached. Fig. 9 shows the 
full arrangement. Now let the lower end 
of the longer tube be put into colored 





m 



Fig. 9. 



AIR. 33 

water, the end of the rubber tube in the lips, and let 
the air be drawn out of the bottle. Then notice a pretty 
little fountain springing up instantly into the bottle. 
There is nothing but air to push the water up. 

These experiments teach us that air resting upon the 
surface of water, or, indeed, of any body, exerts a down- 
ward pressure. 

Ex. 42, — Take the straight glass tube used in Ex. 39 
and push it nearly its whole length under water, and then 
place the finger over one end to close it. Lift the tube 
out of the water, open end downward, and notice that the 
water does not run out of it. There is nothing but air to 
keep it up in the tube. 

Ex. 43. — Take a narrow-necked bottle, and having 
immersed it in a vessel of water until it is filled, almost 
cover it with the finger, turn it mouth downward, and lift 
it out of the water entirely. Notice the water refusing to 
run out, and that there is nothing but air to keep it in. 

Ex. 44. — Take a vj z7?e-mouthed bottle, or an ale-glass, 
and proceed as follows : having filled it with water, slip 
a piece of paper under its mouth and hold it against the 
glass until the bottle is lifted out of the water. 
The hand may then be taken away from the paper, 
when the water will be seen remaining up in the 
bottle. (Fig. 10.) 

In these experiments we see that the air is exert- 
ing upward pressure. 

Ex. 45. — Let the wide-mouthed bottle used in Fig ' 10, 
the last experiment be filled with water and covered 
with the small piece of paper as before. Hold it in a 
horizontal position, see that the water does not run out. 
Turn it around to point in various directions horizon- 

2* 




34: 



PHYSICAL SCIENCE. 



tally; the water is still kept in by the air. Hold it 
obliquely in various directions, and witness the same re- 
sult. We thus see that air exerts pressure in all these 
directions. 

By considering all these experiments on pressure to- 
gether, we are taught that air exerts pressure in all 
directions. 



The Pump. Ex. 46. — Let a glass tube have one 
open end in colored water. "With the lips applied to 
the other end, take the air out of the tube above the 
water, and notice that the pressure of air pushes the 
water up. 

Ex. 47. — Next take a wire longer than the tube and 
wind cotton upon one end until it is so large that it can 
with some difficultv be drawn into the tube. 
Pass the wire up through the tube, and, 
taking hold of the upper end, pull the cotton 
into the other end, and then insert it in the 
colored water. Next pull the cotton upward 
in the tube, and see the water following it. 
(Fig. 11.) Notice that the air is here taken 
out of the tube above the water by lifting the 
cotton. 

We thus learn that water will be pushed up 
in a pipe or tube whenever the air within is by 
any means lifted out. This is the principle of 
the common pump. (Cooley's Philosophy ,p. 31.) 




The Siphon. Ex. 48. — Repeat Ex. 42, and notice 
again that the pressure of air sustains the column of water 
in the tube. (Fig. 12.) Study it further. See that the 
weight of the water is pressing downward; that the 



AIR. 



35 




Fig. 12. 



air is pressing upward, and that the upward pressure is 
strongest. 

Ex. 49. — Take next a glass tube, bent in the 
form of the letter U, its arms being of exactly 
equal length, and immerse it in water. When 
it is completely filled, close one end with the 
finger and lift the tube from the liquid. Hold 
it with open end downward; the water does 
not run out. Close the other end and open the 
first ; the water still remains. 

Now put the forefinger of one hand exactly 
under the middle of the bend so that the tube 

will balance, and then very carefully take the 
finger away from the end of the tube. Both 
ends are now open downward (Fig. 13), but still 
the water does not run out. Notice that the 
water in both arms is pressing downward — that 
the air at both ends is pressing upward. Again, 
see that the downward pressures, being equal, 
overcome equal portions of the air press- 
ures, and thus leave equal upward press- 
ures to keep the water from running out. 

Ex. 50. — -Take next a bent tube, one arm 
being longer than the other. Use it exactly as 
the tube was used in the last experiment. The 
water will not remain in the tube balanced upon 
the finger; notice it running out of the longer 
arm only! (Fig. 14.) 

In this case there is greater pressure of water 
downward in the long arm than in the other; I 
it overcomes more of the air-pressure. This |f 
leaves more of the air-pressure upward against m %- 14 - 
the water in the short arm. This stronger pressure of 




Fig. 13. 




36 



PHYSICAL SCIENCE. 



the air upward against the water in the short arm pushes 
the water up through it, over the bend and out of the 

longer arm. Such a bent tube, one 
arm longer than the other, is called a 
siphon. It is used to transfer liquids 
from one vessel into another; let 
another experiment show how it is 
used, thus : 

Ex. 5 1.— Place an empty jar (fruit- 
can) or other vessel, beside another 
containing water. Fill the siphon 
with water by immersing it, and close the longer arm by 
holding the finger over its end, while the end of the 
shorter arm is being put into the vessel of water. Let 
the longer arm hang over into the empty vessel, and 
open its end. (Fig. 15.) The water will continue to run 
until it stands at the same height in both vessels, (See 
Philosophy, p. 73.) 




Fig. 15. 



The Effect of Heat. Ex. 52. — Take a bottle con- 
taining some colored water, and fit to it a cork 
having a hole in its center. Take the little vial 
and glass tube used in Ex. 36, and pass the tube 
through the hole in the cork of the bottle down 
into the colored water below. (Fig. 16.) !Now 
apply the heat of a lamp-flame gently to the vial, 
or pour warm water over it, and notice bubbles 
of air coming out of the tube and up through 
the water. The vial and tube can no longer hold 
all the air they did. 

Ex. 53. — Press a goblet bottom upward down 
into a vessel of water. See that the goblet is full 
of air. Pour warm water over the goblet, and notice 




air. 37 

bubbles of air coming out through the water, showing that 
the air is made larger by the warmth. These experiments 
teach that the effect of heat upon air is to expand it. 

Ex. 54. — If the bottle and vial, used in Ex. 52, have 
now been standing some time since the heat was applied, 
the air in the vial must have grown cool again. Look at 
the apparatus, and see the colored water standing far in 
the tube above the fluid in the bottle. Notice that the air 
has been cooling and growing smaller at the same time. 

Ex. 55. — Pour now upon the vial some cold water; see 
the water mounting still higher, showing again that as the 
air is cooled it gets smaller. 

We are thus taught that air contracts when heat is 
withdrawn from it. 

Ex. 56. — Place a piece of candle about an inch long — 
perhaps less — upon a flat block of wood. Light it, and 
notice the flame burning steadily. Now put 
a lamp-chimney over the flame, leaving one 
edge of it projecting over the edge of the block 
(Fig. 17), and notice that the flame is no longer 
steady. Its flickering shows that air is coming 
under the edge of the chimney against it. 

Ex. 57. — Now let some bits of light cot- j ( 

ton or feather, hanging at the end of fine I 

thread, be held over the top of the chimney ; *** 1T * 
they will be blown away, showing that air is coming out 
of the top of the chimney. 

We thus learn that heated air is pushed upward by the 
colder air beside it which flows in at the bottom to take 
its place. 

Upon this principle the production of winds may be 
explained. (Natural Philosophy, p. 141.) 




VIBRATIOK 



The Pendulum. Ex. 58.— Let a ball — it may be a 
bullet, a ball of wood, or even an apple — be fastened to 
the end of a cord, the other end of which is to be attached 
to some fixed support above. This fixed support is easily 
arranged by nailing a bar of wood to the window-frame, 
so that it will project out some distance from the wall 
into the room. A string may be bound around the bar, 
and the cord of the ball may be tied into this ring. By 
this means the ball is able to swing freely beneath its 
support. 

A body hung so as to be able to swing freely under its 
support, is a pendulum. 

Ex. 59. — Lift the ball several inches away to one side 
and let it go. Notice it swinging back and forth over 
the same path. Such a motion is called vibration. 

Ex. 60, — Lift the ball again to several inches; let it 
go, and catch it with the other hand just as it reaches the 
point where it would turn to go back ; it has swung once 
over its path. This one motion over its path is called a 
vibration. 

Ex. 61, — Take two balls of equal length, one of lead, 
another of wood, or, such not being convenient, an apple 
and a potato may be used instead, only let them be as 
nearly of equal size as possible. Hang them from £he 



VIBRATION. • 39 

same bar, side by side, with cords of the same length. 
Take one in each hand ; pull them to the same distance, 
and let them both start at the same moment. Notice 
that they go over their paths and get back to the hands at 
the same time, showing that : 

Pendulums of different materials, other things being 
equal, vibrate in the same time. 

Ex. 62, — Take two balls of the same material, two 
apples, for instance, of different sizes, with cords of equal 
lengths. Release them at the same moment ; notice that 
they get back to the hand again at the same time, show- 
ing that : 

Pendulums of different sizes, other things being equal, 
vibrate in equal times. 

Ex. 63. — Take two balls of the same material and of 
the same size, but hang them on cords of different lengths. 
Release them both at once, and notice the short one vibrat- 
ing faster than the other. 

Ex. 64. — Change the lengths of the cords, but still 
have one shorter than the other, and after every change 
notice that the shortest pendulum vibrates most rapidly. 

We thus learn that the time of vibration depends upon 
the length of the pendulum. 

Ex, 65. — Take now two pendulums, one being just 
four times the length of the other.* Count the number 
of vibrations each one makes in one minute by the watch 
or clock. Divide 60 by these numbers, to learn how long 
each one takes to make one vibration. Then notice that 

* Measure from the point of support to a point a very trifle below the 
middle of the ball. 



40 « PHYSICAL SCIENCE. 

the time for the longer pendulum is just two times as 
great as for the shorter. 

Length = 4 Time of a vibration = 2. 

Ex. 66. — Let, next, one pendulum be nine times as 
long as the other. Count and divide as before. Notice 
that the longer pendulum takes three times as long to 
vibrate. 

Length = 9 Time of a vibration = 3. 

Now compare the lengths of pendulums and the times 
of one vibration, and see that : 

The time of one vibration varies as the square root of 
the lengths of the pendulum. 



SOUKD. 



Ex. 67. — Strike the prongs of a tuning-fork gently 
upon the edge of a table, and then stand the other end 
upon the table- top. The sound will be distinctly heard. 
Repeat the operation, and while the sound is heard, bring 
the edge of a knife-blade carefully alongside of one of 
the prongs, and notice what a rattle it causes. The prong 
is found to be in motion, bounding back and forth against 
the blade. 

Ex. 68. — Let a bell be struck, and while the sound is 
heard, touch the bell gently with the finger, &ndfeel the 
tremulous motion while its sound is heard. 

Ex. 69. — If the bell is large, or, better still, if you have 
a glass bell-jar, make a little pendulum of cork, and hang 
it so that it touches the lower rim of the bell. When the 
bell is struck, notice that you not only hear the sound but 
at the same time see the tremulous motion of the ball 
caused by the motion of the bell. 

Ex. 70. — Take a piece of violin-cord, or of piano-wire, 
somewhat longer than your table. Fasten one end to a 
nail in one end of the table, and let the other end of the 
cord pass over a pulley, or even a projecting piece of board, 
fastened to the other end of the table, and to this end of 
the cord hang a heavy weight — a pail or box filled with 
sand or stones. Let two bridges, like the bridge of a 
violin, be placed under the cord near the ends of the 
table. The arrangement is now complete. 



42 PHYSICAL SCIENCE. 

Pull the middle of the cord to one side and let it go 
again. Notice the sound that is heard, and the motion 
that is at the same time seen. 

In all these experiments we find that the sounds of 
bodies are accompanied by tremulous motions or vibra- 
tions, which leads us to infer that : 

Sounds are produced by vibrations. 

Ex. 71.— Move one of the bridges toward the other; 
this shortens the vibrating part of the cord. Make it 
sound again, and notice that while the cord is shorter, the 
sound it makes is higher. Shorten it more yet ; the sound 
is still higher. 

Ex. 72. — Move the bridge gradually back to its first 
position, thus lengthening the vibrating part of the cord. 
Make it sound after every change in length, and notice 
that while the cord is lengthening the sound is gradually 
getting lower. 

We thus learn that the height or pitch of sound pro- 
duced by a cord or wire depends upon its length — the 
highest sound being caused by the shortest cord. 

Ex. 73. — Let the bridges remain stationary, and put 
more and more weight into the box at the end of the cord, 
to stretch it tighter. Notice the sound after every addi- 
tion. It will be found to get higher and higher. 

Ex. 74. — Next take off the weight gradually, so that 
the cord will be stretched less and less, and notice the 
sound after each loss of weight ; it will be found to be 
lower and lower. 

From these experiments we infer that : 

The pitch of the sound of a cord or wire depends upon 
the weight or force which stretches it,— the higher sound 
being produced when the cord is most tightly stretched. 



SOUND. 43 

Ex. 75. — Take two cords of different sizes so that they 
may be of different weights, and stretch them over the 
table side by side. Place the bridges under both cords, 
so that their vibrating parts shall be of equal lengths, and 
finally hang equal weights at their ends. The lighter 
cord will invariably give the higher sound. From this 
we infer that : 

The pitch of sounds produced by different cords depends 
upon their weights. Other things being equal, the lightest 
cord gives the highest sound. 



LIGHT. 



For experiments with light it is very desirable to darken 
the class-room and admit a small beam of sunlight with 
which to work. Choose a window into which the sun- 
light enters most directly at the time the experiments are 
to be made, and prepare it as follows : 

Let some boards be cut of the right length, and let 
them be of such number and length that when fastened 
together by cleets they will form a shutter fitting the in- 
side of the window and darkening it completely. At a 
convenient distance from the bottom of this shutter a hole 
two or three inches in diameter should be made, through 
which sunlight may come. For some experiments the 
direction of the beam of light passing through the room 
is a matter of importance. An addition easily made to 
the shutter will help the operator to control the direc- 
tion and change it at will. Let a shelf be fastened to the 
outside of the shutter, just under the hole. Upon this shelf 
a piece of looking-glass may be placed. Now, by propping 
up the outer end of this glass, and perhaps one side of it 
also at the same time, it may be given just the right posi- 
tion to receive the sun's rays and throw them through the 
hole into the room. Any change of position of the glass 
will change the direction of the light. That the glass 
may be easily changed at pleasure, have a second hole in 
the shutter large enough to allow the hand to pass out for 



LIGHT. 45 

the purpose : this hole may be covered with black cloth 
when not in use. 

It will not be difficult to darken the othdr windows in 
the room by closing shutters, or drawing curtains, or 
perhaps by hanging shawls over them. 

With this cheap* and easily- constructed arrangement 
many very beautiful experiments may be made with the 
greatest ease. A looking-glass, a small concave ?nirror, a 
convex mirror, one convex lens and another concave, and 
a glass prism, are the most important pieces of apparatus. 
They can be obtained from apparatus dealers at small 
cost. 

A little time, a little money, and a little ingenuity 
spent in putting up and using this apparatus, will be 
abundantly repaid in beautiful results. 

Choose a day when the sun shines brightly, and while 
making experiments keep the lower sash of the window 
raised above the hole. 

Ex. 76. — Through the hole in the shutter admit the 
sunbeam : sprinkle dust in the path by striking two dust- 
brushes together in front of its entrance. Notice the path 
of the sunbeam shown by the very beautiful bar of illu- 
mined dust : it is perfectly straight. 

Ex. 77. — Change the inclination of the looking-glass a 
little, and see the change of direction of the sunbeam in 
the room. But notice that in every position the beam of 
of light is straight. 

We thus learn that light -travels in straight lines. 

Ex. 78. — Hold the convex lens in the beam of light 
entering the room, and see what a curious change : Notice 
that the light is brought to a point (Fig. 18) at some 




46 PHYSICAL SCIENCE. 

distance from the lens, and that beyond this point it 

widens out again. 

A point where light is col- 
lected is called a focus. The 
cone of light going toward the 
focus is called a pencil of light : 
the cone going from the focus is 
also a pencil. In the first case 
the pencil consists of converging 
rajs; in the second the pencil 
Fig- is. consists of diverging rays. 

Ex. 79. — Place a lighted lamp or candle on a table in 
the darkened room. Hold. a flat piece of wood, two or 
three inches in width, at a convenient distance in front 
of the flame and catch its shadow upon a white wall or 
upon a piece of white cloth about as far from the wood 
as the wood is from the flame. Notice that the shadow 
is made up of two distinct parts — a dark center and a 
much lighter fringe on each side. 

Ex. 80. — Form shadows of other bodies in the same 
way — it scarcely matters what is chosen for the purpose. 
The two parts of the shadow will in every case be more 
or less distinct. 

Now the dark center is called the umbra and the 
lighter envelope is called the penumbra. Every shadow 
is made up of these two parts. 

Ex. 81. — Place two flames upon the table a little dis- 
tance apart, and hold the flat piece of wood in front of 
them, and notice that two shadows appear upon the wall 
or screen. 

Ex. 82.— Then move the wood gradually toward the 
screen and notice the two shadows drawing nearer to- 



LIGHT. 47 

gether. At length the two shadows will lie right beside 
each other. Carry the wood a little farther, and the two 
shadows begin to overlap each other, and we may notice 
then a single shadow made up of the two, its umbra and 
penumbra very distinct. 

The umbra in the last experiment is the part of the 
shadow which gets no light from either of the flames ; the 
penumbra receives light from one or the other, and is not 
so dark in consequence. 

Just so the umbra in a common shadow is the part 
which gets no light from any part of the flame which 
casts it, while the penumbra is the part which receives 
light from some part of the flame, and is not so dark on 
that account. 

Ex. 83. — The " dance of the witches " may be shown 
by cutting fantastic figures out of heavy card-board and 
hanging them by slender rubber cords from a bar of wood, 
by which they can be held between the flame and the 
screen. A dancing motion can be easily given to these 
figures, and the motion of their shadows will present an 
amusing spectacle to those sitting in front of the screen. 
Two or three flames a little distance apart will multiply 
the shadows and increase the amusement. 

Ex. 84. — A circular disk of card-board, a triangular 
piece of wood, a cubical block, a ball, and bodies of other 
shapes, may be in turn held in front of a flame and their 
shadows formed. Notice the shapes of the shadows : they 
will change with every change in the position of the ob- 
ject. The disk, for example, gives a circular shadow 
when its side is toward the light, but only a dark line 
when turned edgewise. The ball, however, will give a 
circular shadow in all positions. 

The sphere is the only form which will in all positions 



4S 



PHYSICAL SCIENCE. 



give a circular shadow. The earth's shadow on the moon 

in an eclipse always has a circular oittline, showing that 

the earth is a sphere. 

Ex. 85. — Let a beam of sunlight into the darkened 

room and hold a looking-glass obliquely in its path : the 
light will be instantly thrown from the 
glass toward the ceiling or wall of the 
room., (Fig. 19.) If the air is well 
sprinkled with dust, the bars of light 
striking the glass and thrown from its 
surface will be seen distinctly. 

Ex. 86. — Hold a piece of bright tin 
or of any polished metal in place of the 
glass, and notice the same result. 

The light which falls upon the surface 
of a body is called the incident light: 

that which is thrown off is called reflected light. 




Fig. 19. 



Ex. 87. — Place a looking-glass upon the floor with its 
face uppermost, and upon a thick block of wood, or a 
book on the floor, near one end of the mirror, put a 
lighted candle. Standing on the other side of the glass, 
move around until the image of the candle is distinctly 
seen. 

Ex. 88. — If the room is not darkened you may stand a 
goblet partly filled with water upon the face of the 
looking-glass, and then see the goblet standing upon its 
image — one goblet seeming to stand erect upon another, 
bottom upward partly full of water. 

Notice in these experiments that every part of the 
image is just as far behind the looking-glass as the cor- 
responding part of the object is in front of it, and that 
the image is just as large as the object. 



LIGHT. 49 

It is the light going from the object to the glass, and 
being reflected from its surface to our eyes, that enables 
us to see the image. 

Ex. 89. — Take two looking-glasses of considerable size 
and stand them upon their edges at right angles to each 
other on the table, the room not being darkened. Let a 
vase of flowers or any other convenient object be placed 
between the two glasses. Three distinct images of the 
object will be seen. 

Ex. 90. — Make the opening between the glasses much 
less than a right angle, and then put your face half-way 
between their ends and laugh, as few ever fail to do, at 
the circle of faces which is seen in the mirrors — a " sur- 
prise party," every member of which will laugh with 
you. 

Ex. 91. — Take a bowl or basin in the dark room, and 
at a little distance from it put a candle-flame, so that its 
light may pass over the top 
and strike the opposite side 
just at the bottom, (a, Fig. 




20.) The whole bottom 

will then be in the shade, 

and will look much darker 

than the side on which the Fig. 20. b a 

light shines. Then pour water into the bowl until it is 

nearly filled. Notice that the light now covers a part of 

the bottom (a b) of the vessel. 

We see that in this case the light is bent out of the 
straight line on entering the water. Such a bending of 
light always occurs when light passes from one substance 
into another : it is called refraction. 
3 




50 PHYSICAL SCIENCE. 

Ex. 92, — The room being light, put a penny at the 
bottom of the empty bowl, so that as you look over the 

edge of the vessel it is 
just out of sight (at a, 
Fig. 21). Now pour 
water into the bowl 
carefully, so as not to 
disturb the penny. The 
penny will very soon 
Fig. 2i. come into view (at b), 

no change having occurred in the position of the vessel, 
penny, or eyes. 

Remember that we see the penny just as we see every 
thing else, by light that comes from it to our eyes. With- 
out the water, this light, coming up over the edge of the 
bowl, goes above the eye / for this reason we do not see 
the penny. But when it has to come up out of water the 
light is bent where it enters the air, and then, coming 
over the edge of the bowl, can enter our eyes and enable 
us to see the penny. 

Ex. 93. — Let a convex lens — a spectacle glass can be 
used with success — be placed in the opening in the 
shutter of the dark room. The hole should be no larger 
than the lens : it can be made smaller, if need be, by cut- 
ting a hole of the right size in a piece of card-board, and 
then tacking this card over the larger hole in the shutter. 
Let a screen be made of thin white muslin stretched over a 
wooden frame. Place this screen near the lens, and move 
it back and forth until the best effect is found. A beau- 
tiful inverted picture in miniature of all things outside 
the window will be seen upon the screen. A sheet of 
white paper may be used instead of the muslin screen ; the 
picture will then be best seen on the side toward the lens. 



HEAT. 



Production of Heat. Ex. 94.— Rub a metallic but- 
ton upon a smooth board briskly; it soon will become 
quite hot. 

Ex. 95. — Let the finger of the right hand be pressed 
upon the coat-sleeve of the other arm, or upon a piece of 
woolen cloth fastened to the desk or table, and then 
rubbed briskly back and forth. An inconvenient heat is 
soon felt. 

We thus learn that heat is produced by friction. 

Ex. 96. — Let a nail be laid upon some hard surface, a 
smooth stone, or a flat-iron, for example, and then let it be 
struck several blows with a hammer in quick succession. 
On feeling the nail, it will be found to be considerably 
warmed. Indeed, it can, in this way, be made too hot to 
be handled conveniently. 

We thus learn that heat is produced by blows. 

Ex. 97. — Upon some large fragments of quick-lime 
lying on a plate, pour some water. After a few minutes, 
notice the lime swelling and crnmbling to powder, while 
large volumes of steam are escaping. Let the hand be 
held in this steam only for an instant, or be laid upon the 
plate when the action has ceased, and great heat will be 
discovered. 



52 PHYSICAL SCIENCE. 

The action of the lime and water is called a chemical 
action, because the nature of these bodies is changed. 

Ex. 98. — Into a cup put a small quantity of cold water, 
and then add about one-fourth as much oil of vitriol. 
The mixture will become intensely hot. There is a chem- 
ical action between the two fluids. 

From these experiments we learn that heat is produced 
by chemical action. The heat of all our lamp-flames and 
furnaces is produced by chemical action. 

Conduction of Heat. Ex. 99. — Take an iron wire 

and press a bit of wax against one side of it at a distance 

of a few inches from one end. Place 

m this end in the flame of a lamp. (Fig. 

%2.) After a few minutes the little 

bit of wax, all this time clinging to 
Fig. 22. t } ie w j re ^ w iu f a n ff # ]sj- OW5 tne j ieat 

must have travelled from the flame gradually along the 
wire until it reached the wax, and then, by melting it, 
caused its fall. 

Ex. 100. — Hold one end of a brass rod, a few inches 
long, in the lamp-flame. After a little waiting the rod in 
the fingers at the other end feels warm. In this case the 
heat has evidently travelled gradually from the flame 
through the rod to the fingers. 

When heat travels from particle to particle gradually, 
as in these experiments, it is said to be conducted. The 
body in which it travels is called a conductor. 

Ex. 101. — Take the stem of a tobacco-pipe and a rod 
of iron as nearly of the same size as possible, and place 
their ends together, lapping them about an inch, and 
binding them firmly with small wire. Next fasten a ball 
of wax to the under side of each of the rods, equally 





HEAT. 53 

distant from the middle point of their junction. Now, if 

this arrangement is held with the junction in a lamp 

flame (Fig. 23), it will not be , 

long before the ball of wax is 

melted from the iron, but it 

will take a long time indeed 

to melt the ball from the Fig * 23 V 

pipe-stem. We learn thus that the iron conducts heat 

better than the pipe-stem. 

Ex. 102. — Take two wires of different metals, brass 
and copper, for example, of the same size and length. 
Hold one wire in each hand, the other end of the wire 
being in the lamp-flame. The heat will be found to reach 
the fingers through one of the wires quicker than through 
the other. The two metals teach us that they do not 
conduct heat alike. 

Ex. 103. — Let two spoons, one of German silver, the 
other of silver, be put into the same cup of hot water, 
with their handles projecting. Feel of the upper ends 
from time to time, and notice that the silver spoon is 
heated quickest. 

From these experiments we learn that all bodies do not 
conduct heat alike. 

Convection of Heat. — Ex. 104. — Fill a glass flask 
two- thirds full of water, and place it upright in a shallow 
basin of sand standing on a hot stove. Yery soon one 
who looks closely at the water will see delicate currents 
moving upward from the bottom. Drop a bit of blue 
litmus into the water. It falls to the bottom and slowly 
dissolves. Blue clouds appear, which, wafted upward by 
the currents of water, enable us to see their motion dis- 
tinctly. These upward currents are of warm water, and 



54 PHYSICAL SCIENCE. 

the lieat is being distributed throughout the water in the 
flask by their motion. 

When heat travels by means of currents in the body 
receiving it, the process is called convection. 

Radiation of Heat. — Ex. 105. — Heat an iron ball 
or a piece of stone in the stove until nearly or quite red- 
hot. Let it be brought out into the room by means of a 
pair of tongs. Hold the hand at a little distance above it, 
on one side of it and on another, and below it. Notice 
that instantly, no matter in what direction, the heat of 
the ball is felt. The air is a very poor conductor, but we 
find heat going through it in all directions more swiftly 
than it can go through the very best conductor. 

Heat that is thrown through poor conductors in all 
directions is said to be radiated, and the process of dis- 
tributing heat in this way is called radiation. 

Expansion by Heat. Ex. 106. — Take a bottle hav- 
ing a ground stopper. When the stopper is out, warm 
the neck of the bottle gently by wrapping a cloth wet 
with warm water around it, and afterward put the stopper 
in — not too tightly — just so that it fits the neck nicely. 
Let the neck cool again, and when cold try the stopper. 
Notice that it is tightly held — perhaps it will not come 
out at all, because the neck of the bottle is so small as to 
grasp it too closely. Now wrap the neck again in the 
warm cloth, and after a little try the stopper; notice that 
it comes out easily. The heat seems to have made the 
neck larger, so as to let the stopper out. 

Ex. 107. — Let a hole be bored through a piece of hard 
wood, just large enough to allow a bullet or other metallic 
ball to pass through, closely touching its sides. An iron 



HEAT. 55 

rod may be used instead of a ball often more conveniently. 
Heat the ball or rod, and before it gets hot enough to 
burn the wood, try to pass it through the hole. If it has 
been warmed enough you will notice that the hole is no 
longer large enough to let the body pass. 

These experiments teach us that heat expands or en- 
larges solid bodies. 

Ex. 108. — Fill a bottle with cold water. Pass a piece 
of glass tube, a few inches long, through a cork fitting the 
neck of the bottle nicely, and press the cork into 
the neck. If the bottle was brimfull of water, as 
it ought to be, the water will stand some distance 
up in the tube when the cork is inserted (Fig. 24). 
Tie a string around the tube to mark the height 
of the water in it. Now plunge the bottle into a 
vessel of warm water. Notice the water quickly 
beginning to rise up the tube, and continuing to 
do so while the heat is applied. 

We see that the water is getting larger as it 
becomes hotter. Fig. u. 

Ex. 109. — Another bottle, used in the same way, with 
some other liquid, as oil or alcohol, will show the same 
effect ; the liquid will get larger as it gets warmer. 

From these experiments we learn that heat expands 
liquid bodies. 

Ex. 110. — Fit the neck of a bottle with a cork, and 
through this cork put the ^nd of a glass tube several 
inches long. Into another bottle put some water, which 
may be colored with ink, or cochineal, or litmus. Turn 
the first bottle bottom upward, and put the open end of 
its tube down into the colored water of the second. 




56 PHYSICAL SCIENCE. 

Notice, before going farther, that the upper bottle and its 
tube are full of air. Next pour warm water upon the 
upper bottle, and notice numerous bubbles of air escaping 
through the fluid from the lower end of the tube. The 
air is expanded by the heat, 

Ex. 111. — After a little time, the colored water will 
rise some distance up the tube in the arrangement used in 
the last experiment. When this is the case, notice that 
the tube, above the water, and the bottle are full of air. 
Now pour some warm water again over the bottle, and 
see the water quickly driven down by the expanding air. 

We thus learn that heat expands air, and when similar 
experiments have been made with other gases, the general 
truth is found that heat expands gaseous^ bodies. 

Contraction by Cooling. Ex, 112. — The hot rod 

of iron (Ex. 107) was too large to go through the hole in 
the hard wood, but now that it is cold again, try i£? and 
notice that it goes through easily again. It has given 
off its heat and at the same time grown smaller. 

Ex. 113. — Take the bottle and tube with water, used 
in Ex. 108; mark the height of the water in the tube, 
and then place the bottle in a vessel of cold water. Notice 
the water falling in the tube, showing that as the water in 
the bottle cools it grows smaller. 

If this does not show distinctly the desired result, then 
first warm the bottle of water, and afterward put it int 
the vessel of cold water. 

Ex. 114. — Take the apparatus used in Ex. 52, the col- 
ored water now standing some distance up in the tube, 
the space in the tube above the water and in the bottle 
being filled with air. Pour cold water upon the upper 
bottle, and notice the colored water quickly rising higher 



HEAT. 5f 

in the tube. The air is cooled by the water, and we see 
that it at the same time gets smaller. 

From these experiments we learn that the withdrawal 
of heat from bodies causes them to contract. We thus 
find that the hotter a body is the larger it is, and the con- 
trary—the colder it is, the smaller. 

Curious effects in Water. Ex. 115.— Into a com- 
mon bowl or basin put a considerable quantity of snow, or 
ice shaved fine with a large knife, and add about half as 
much common salt. Stir the mixture thoroughly ; it will 
become nearly fluid and be intensely cold. It is called 
a freezing mixture. Fill a thimble with water, or a pipe- 
bowl, with the hole in its bottom closed with wax, and 
stand this little dish in the freezing mixture. The water, 
after a few minutes, will be frozen. 

Ex. 116. — Now take the bottle and water (Ex. 108), 
the fluid standing some distance up the tube, and place it 
in the freezing-mixture. 

Notice first, that the fluid sinks in the tube, showing 
that as the water cools it contracts. 

Notice next, after a little time the fluid stops sinking, 
showing that as water goes on cooling more yet the con- 
traction stops. 

Notice again, that the water begins to rise in the 
tube again, showing that the cooling water is now ex- 
panding. 

Notice finally, that ice begins to form in the bottle, and 
that while the water is freezing, the water in the tube 
continues to rise, showing that water expands while 
freezing. 

Ex. 117. — Take now the bottle containing ice from 



58 PHYSICAL SCIENCE. 

the freezing-mixture, and put it into a vessel of water 
slightly warm. 

Notice the water sinking in Jthe tube while the ice is 
melting, showing that heat contracts the ice while it 
melts it. 

Notice afterward, that the water continues to sink in 
the tube for a little time, showing that heat applied to ice- 
cold water contracts it. 

Notice finally, that the water in the tube begins to rise 
again, showing that after water has reached a certain 
degree of temperature, heat expands it. (See Natural 
Philosophy, p. 240.) 



ELECTRICITY. 



The successful performance of experiments in electricity 
demands a dry atmosphere and dry material : dampness in 
either may cause annoyance and even complete failure. 
The winter season is generally more favorable than the 
summer, and an un ventilated room, in which the air is 
loaded with moisture from the lungs of many individuals, 
is to be especially avoided. In a long, cold winter even- 
ing, when the family are gathered around the cheerful 
sitting-room fire, electrical experiments are most likely to 
succeed admirably. And in a school-room, which has 
been thrown open and well-ventilated during recess, and 
in which a brisk fire is rapidly heating the atmosphere 
again, or, better still, in the morning before the pupils 
have had time to load the air with dampness, electrical 
experiments may be tried with the best assurance of 
success. 

The following experiments are simple enough for a 
child to perform, and will furnish children not only, but 
older students as well, with much amusement and in- 
struction. 

Electricity produced by Friction. Ex. 118. — 

Take a piece of thin and tough brown paper, about an 
inch wide and six inches long; heat it thoroughly by 
holding it over a hot stove or the flame of a lamp, and then 
holding it in one hand by the end, quickly pull it between 



60 PHYSICAL SCIENCE. 

the thumb and fingers of the other hand, thus rubbing it 
vigorously. After two or three such rubbings bring the 
paper near to the wall, and it will instantly fly into con- 
tact with it, and perhaps if you let go of it you will see 
it clinging to the wall. It will thus remain sometimes 
for several minutes as if pasted. 

Ex. 119. — Rub the paper a second time, and, holding 
it by one end in one hand, bring the other hand alongside 
of it Notice how quickly the paper flies against the 
fingers, and how strongly it is inclined to stay there. 

Ex. 120. — Procure a glass tube several inches in 
length, — a lamp-chimney, if one can be found of conve- 
nient shape to rub easily ; procure also a piece of flannel 
cloth. Both should be thoroughly dry. Holding the glass 
in one hand, bring it up very near to the face ; you will 
be able to notice no effect. Next rub the glass vigorously 
with the flannel held in the other hand, and bring it after- 
ward near to the face as before. A sensation will now be 
felt like what would be caused by drawing spiders' webs 
over the face. 

Ex. 121,-^Eub the glass again vigorously, and after- 
ward bring it near to the knuckle of your hand ; a crack- 
ling sound will be heard, and in the dark little sparks of 
light are often seen. 

Ex. 122. — Place some very small and light bits of 
cotton upon the table. Thoroughly rub the glass again, 
and bring it near to the bits of cotton ; notice how quickly 
they leap up to meet it. 

Ex. 123. — Let a bit of cotton or downy feather be 
floating in the air ; bring the glass, which has been vigor- 
ously rubbed, near to it. The cotton or the feather w T ill 
instantly dart against the glass through considerable dis- 
tance. 



ELECTRICITY. Ql 

Ex. 124. — Any one of the preceding experiments may 
be made with a stick of sealing-wax in place of the glass 
tube. The same effect will be produced. 

In these experiments we see that by rubbing the paper, 
the glass, or the sealing-wax, a new power seems to be 
developed in them. All the effects noticed are due to 
electricity, and this electricity is in such cases produced 
by rubbing, or, as it is called, by friction. 

Attraction and Repulsion. Ex. 125.— Untwist a 
silk thread, and take one of its fine fibres ; tie to the end 
of this a very small and light piece of cotton. Let another 
person hold the cotton by taking hold the other end of the 
thread, while you rub the glass tube vigorously. Then 
bring the tube near to the bit of cotton. You will see 
the cotton fly quickly toward the glass, sometimes through 
a distance of several inches. The cotton is attracted by 
the glass. 

Ex. 126. — Rub the glass thoroughly again, and again 
bring it near the cotton ; the cotton will doubtless be 
attracted as it was before. If so, let it cling to the glass 
for some time; then rub the tube again and present it to 
the cotton as before. If the cotton is again attracted, let 
it stay in contact with the glass for a time, and then go 
over the same work again. After a few, — sometimes only 
one of these trials, the cotton will refuse to again come in 
contact with the glass. As often as the tube is moved 
toward it, the cotton darts awav. Not until it has first 
touched some other body can the cotton be made to touch 
the glass. 

In this experiment we find the cotton driven away from 
the glass tube ; it is said to be repelled. 

Ex. 127. — Sometimes the electricity may be made bo 



62 PHYSICAL SCIENCE. 

strong on the glass that placing it on one side of the sus- 
pended cotton and the hand or piece of iron on the other 
side of it, the little pendulum will fly quickly back and 
forth between them many times, being first attracted and 
then repelled by the electrified glass. 

We learn from these experiments that electricity shows 
its presence in two ways, viz. : by attraction and repul- 
sion. 

Ex. 128. — Let a long silk ribbon, warm and dry, be 
hung over the forefinger of the left hand ; the t-wo parts 
will hang down side by side together. Now put the fore- 
finger of the other hand between the two parts of the 
ribbon and press them tightly against it with the thumb 
and other fingers. Pull the ribbon out quickly, rubbing 
the whole length of its parts between the fingers ; repeat 
this operation three or four times, and then notice that 
the two parts of the ribbon will no longer be willing to 
touch each other. They repel each other. Put the hand 
between them, and both quickly fly toward it; remove 
the hand, and they as quickly fly back again. 

Ex. 129. — Let one person rub the ribbon, as in the 
last experiment, while another rubs the stick of sealing- 
wax with the dry flannel. When both are well electri- 
fied, let the sealing-wax be brought between the parts of 
the ribbon. They will fly still farther apart. The electri- 
fied sealing-wax repels the electrified ribbon. 

Ex. 130. — Now rub a glass tube, a lamp-chimney, if 
of convenient shape, and bring it between the electrified 
branches of the ribbon. Both parts instantly fly toward 
the glass; the electrified glass attracts the electrified 
ribbon. 

We see that the ribbon acts differently toward the 



ELECTRICITY. 63 

electrified glass and toward the electrified sealing-wax. 
It flies toward the first, and from the second. 

Ex. 131. — Hang a little ball of cotton to the end of a 
silk fibre, as in Ex. 125. Rub the glass, and then bring it 
in contact with the ball until the latter flies away, being 
repelled by the electrified glass. Rub the sealing-wax 
with flannel, and bring it toward the ball ; the ball will 
quickly fly to meet it, being attracted by it. Again, we 
see that electrified glass and electrified sealing-wax act in 
different ways ; w T hen the cotton is repelled by glass it is 
attracted by sealing-wax. 

Now whenever the electricity is like that produced by 
rubbing glass it is called positive electricity, and when it 
is like that produced by rubbing sealing-wax with flannel 
it is called negative electricity. 

The Electroscope. Ex. 132. — Rub the glass tube 
or stick of sealing-wax vigorously, and observe whether 
any visible change whatever is produced. None : then, 
without somefarther trial, it is not possible to tell whether 
electricity has been developed or not. 

It may be brought near to the face or hand, and the 
feeling of cobwebs, or a snapping sound, may show that 
the tube or wax is electrified, or bringing it near to light 
bodies, as cotton, on the table, electricity will show its 
presence by attracting them. But neither of these ways 
is always quite convenient. 

Ex. 133. — Now take a slender rod of some dry wood, 
several inches long; make a little ball of the dried pith 
of corn-stalk or elder, of cork, or even of cotton ; fasten 
it to one end of a silk fibre, and tie the other end of the 
fibre to the other end of the wooden rod. Next place the 
rod upon the table, so that the end carrying the ball shall 



64 PHYSICAL SCIENCE. 

project some inches beyond the edge, or, what is better 
yet, put the wood up on a pile of books, or some other 
support, above the table, so that the little ball may swing 
clear. 

Now notice that whenever the electrified glass tube or 
sealing-wax is brought near to this little pendulum, the 
electricity is at once shown by the motions of the ball, 
which, if the electricity is well developed, will fly toward 
the tube or wax, and, after a moment's hesitation, will 
as quickly fly away again. 

Ex. 134. — Or, take tinfoil,* — a piece one-half inch 
long and one-quarter inch wide, and hang it in place of 
the ball in the preceding experiment, and it will be found 
to show the presence of electricity as well as the other. 

Here then notice these simple and convenient arrange- 
ments by which to show the presence of electricity. Any 
such instrument is called an electroscope. 

Ex. 135. — Rub the glass tube vigorously, and then 
bring it in contact with the ball of the electroscope ; this 
ball, remaining in contact only a moment, if the tube is 
well electrified, flies away again. We have seen this 
action in former experiments, but what we wish to notice 
now is that the ball in contact with the glass takes elec- 
tricity from it, so that it is electrified in the same way as 
the glass, or in other words, positively, and that when this 
is the case, the two bodies separate, showing that they 
repel each other. 

In this experiment we see that two bodies, electrified 
with positive electricity, repel each other. 

Ex. 136. — Next rub the sealing-wax vigorously with 
flannel, and hold it in contact with the ball of the elec- 

* The thin metallic wrapping found on some kinds of packages at the 
grocery store. 



ELECTRICITY. 65 

troscope until it flies away, as it will do after one or more 
trials. Now what we must notice here is that the elec- 
tricity of the sealing-wax is negative, and that the little 
ball must have the same kind of negative electricity also 
in it when it flies away from the wax. 

In this experiment we see that both bodies, electrified 
with negative electricity, repel each other. 

We see from these two experiments that when bodies 
are electrified in the same way, they repel each other. 
Call this the 1st Law, 

Ex, 137. — Rub the glass tube again, and electrify the 
ball of the electroscope with it. Notice that the little 
ball is positive, because electrified from glass. Then rub 
the sealing-wax with flannel, and bring it near to the 
little ball. The ball darts instantly against the wax. The 
wax is negative, the ball is positive, and the two attract 
each other. 

Here we see that two bodies, electrified with opposite 
kinds of electricity, attract each other. Call this the 2d 
Law. 

Ex. 138.— Repeat the experiment with the silk ribbon 
(Ex. 128). Notice its two branches repelling each other. 
Now, are these branches electrified with the same or with 
opposite kinds of electricity ? (1st Law.) 

Ex. 139. — Can we find out which hind of electricity 
we have in the silk ? 

Rub the glass tube, and hold it in contact with the ball 
of the electroscope until it flies away. We know that the 
ball is positive. Bring the silk ribbon, whose branches 
are repelling each other, near to the positive ball, and see 
how quickly the two fly together ! The positive ball is 



66 PHYSICAL SCIENCE. 

attracted, and hence (2d Law), the silk must he nega- 
tive. 

We see then that our little " electroscope " not only 
helps ns to detect the presence of electricity; it also 
helps ns to tell which kind a body is electrified with. 
Let us try it. 

Ex. 140, — Take a piece of thin but strong brown 
paper ; cut from it a strip an inch wide and sixteen or 
twenty inches long; thoroughly dry and warm it, and 
then use it just as the silk ribbon was used (Ex. 128). 
After the branches of the paper have been drawn through 
the fingers once or twice, they repel each other strongly. 
Now w^hat kind of electricity have they ? Electrify the 
ball of the electroscope from the sealing-wax rubbed w T ith 
flannel ; the ball is then negative. Bring near the ball 
the paper, and see how strongly they repel each other, 
showing (1st Law) that they are in the same condition ; 
the paper is negative. 

Ex. 141, — Electrify the ball of the electroscope from 
glass: it is positive. Now rub the sealing-wax withj^im- 
nel, and notice that it attracts the ball, showing the wax 
to be negative. 

Pass the hand over the surface of the sealing-wax to 
remove the electricity from it, and then rub it vigorously 
with a piece of silk. Electrify the ball of the electro- 
scope from the glass again ; it is positive. Bring the 
electrified wax near to it, and then notice that it now 
repels the ball, showing the wax to be positive. It ap- 
pears that the electricity of sealing-wax, when rubbed 
with flannel, is positive, but, when rubbed with silk, is 
negative ! 

Ex. 142. — See whether the electricity of glass is differ- 
ent when the rubber is flannel from that when the rubber 



ELECTRICITY. 67 

is silk. To do this electrify the little ball from the 
sealing-wax, rubbed with flannel, and bring the electri- 
fied glass near to it. 

Ex. 143. — Take two pieces of brown paper, each 
about ten inches long by five inches wide; make them 
quite hot by holding them over a heated stove or the 
flame of a lamp. Place them on the table, or, still 
better, on a tea-tray, one above the other, and rub them 
vigorously with the palm of the hand. If now you take 
hold of one corner and lift them from the table, you will 
find them clinging to each other. If you try to separate 
them you will see how strongly they attract each other, 
and sometimes you may hear also a crackling sound on 
pulling them apart. 

Notice that the upper one only was rubbed but that 
both are electrified. And more, since they attract each 
other they are electrified in different ways. 

Ex. 144. — Take two fresh sheets of paper, such as 
described in Ex. 143, and, having heated them thoroughly, 
put one above the other on a pane of glass. Rub the 
upper sheet vigorously with the hand. Taking hold of 
one end, lift them from the glass, and notice that they 
now repel each other. 

If Experiments 143 and 144 are repeated, it will be 
found that the papers whenever rubbed while lying upon 
the tea-tray will attract, but if rubbed while lying upon 
the glass they repel each other. 

Now the upper one only is electrified by the rubbing ; 
the lower one is electrified from the upper one. When 
they lie upon glass the lower one becomes electrified in 
the same way as the upper one, and hence they repel (1st 
Law), but when they lie upon the tea-tray the lower one 



68 PHYSICAL SCIENCE. 

becomes electrified in the opposite way, and hence they 
attract (2d Law). 

When one electrified body electrifies another body near 
to it, and puts it into a condition opposite to its own, it is 
6aid to act by induction. The upper strip of paper, when 
they were rubbed on the tea-tray, electrified the lower 
one by induction. 

The fall explanation of induction, or, as it is now gen- 
erally called, polarization, may be left for a higher course 
of study. 

Ex. 145. — Having electrified the two sheets of paper, 
show that they are in opposite conditions by testing them 
with the electroscope. 



EAST EXPERIMENTS 



IS 



CHEMISTRY. 



OHEMISTET. 



The following simple experiments in Chemistry are 
pretty and instructive, but, as a general thing, the mate- 
rials needed are not so conveniently obtained as those 
needed for the experiments in Natural Philosophy. They 
are not expensive, however, and what cannot be found at 
the village stores can be sent from dealers in larger towns 
on application. 

Chemical Action. Ex. 146. — Put some strong vine- 
gar into a goblet — enough to fill it about one-quarter full. 
Take some common " baking soda," as much as will lie 
upon the end of a case-knife blade, and sprinkle it into 
the vinegar. A violent foaming w r ill occur, continuing 
for a time, and when it stops the "soda" will have dis- 
appeared. Add more " soda," little by little, until the 
fluid refuses to foam; the "soda" last added will then 
remain in the bottom. Now notice: the soda has dis- 
appeared from view in this action, while the vinegar (touch 
it w^ith the tongue) is so changed as to be no longer sour. 

Here then we find a violent action going on between 
the vinegar and the soda, by which the natures of both 
these substances are changed. 

Ex. 147. — Into a common bottle put a few small 
pieces of copper, and then pour in upon them nitric acid 
enough to cover them. Notice that a violent action 
quickly begins. The fluid appears to boil. Its color be- 



72 PHYSICAL SCIENCE. 

comes deep blue. Cherry-red vapors fill the bottle above 
the fluid, and perhaps run over the top of it into the 
room. The copper is, in the mean time, being slowly 
used up: it will finally disappear altogether if there is 
acid enough used for the purpose ; and when the action 
ceases, there will remain the quiet blue liquid in the 
bottle, with some of the red vapors remaining in the air 
above. 

In this experiment we again find a violent action, by 
which the nature of the substances used is changed. 

Ex. 148. — Into one goblet put three or four drops of 
hydrochloric acid: into another put as much ammonia. 
Now turn one of these goblets right bottom side up 
over the mouth of the other. Both will be quickly filled 
with white fumes. The acid and the ammonia are liquids 
nearly or quite colorless : they form, when put together, a 
vapor which is white. 

Here also we notice an action which changes the nature 
of substances. 

Ex. 149. — Mix together a half-teaspoonfull each of 
sugar and potassic chlorate, both powdered, and put the 
mixture upon a common card. The card may well be 
laid upon the top of a goblet for support to keep it off the 
table. Now put two or three drops of sulphuric acid 
upon the mixture. A curious combustion will quickly 
follow, in which tongues of purple flame will shoot up 
some distance with considerable noise. 

When the burning is over, look for the sugar and the 
chlorate : both have disappeared, and nothing but a black 
coal-like mass remains upon the card instead. 

We notice that this combustion is an action by which 
the natures of the burning bodies are changed. 

Now, all such actions as have been shown in these ex- 



CHEMISTRY 73 

periments are called Chemical Actions. We therefore 
mean by the term chemical action any action among 
bodies of matter by which their natures are changed. 

Combination and Decomposition. Ex. 150. — 

Into a small vial — a long and narrow one is best for the 
purpose — J3ut some water, and then add oil enough to 
cover the water well. Being the lighter liquid, the oil 
of course floats upon the water. Now pour in a little 
ammonia and shake the mixture thoroughly. A soapy 
liquid will appear instead of the oil and water. Indeed, 
the oil and the ammonia have joined themselves together 
and made a kind of soap which mixes with the water. 
Notice that this new substance, the soap, is a very differ- 
ent thing from either the ammonia or the oil which 
make it. 

Now, when two or more substances disappear to form 
a new one different from themselves, they are said to 
combine. The new substance made is called a com- 
pound. The ammonia and the oil have combined to 
form the soap, which is a compound. 

Ex. 151. — Add to the soapy liquid just made in Ex. 
150, a little strong sulphuric acid. Shake them well 
together. The soapy liquid will in part or wholly dis- 
appear, while the oil will be brought back again and will 
be seen floating upon the water as before. Now we see 
that the sulphuric acid must have taken the ammonia 
away from the oil, for the soapy substance is broken up, 
the oil in it 'coming back again. 

When a substance is separated into the different ma- 
terials which compose it, as the soap has been in this 
experiment, it is said to be decomposed. The substances 
into which it is separated are called its constituents. The 



74 PHYSICAL SCIENCE. 

soap was decomposed ; oil is one of its constituents, am- 
monia is another. 



Acids. Ex. 152. — Crush one or two small pieces of 
blue-litmus and put the powder into a goblet of water. 
The litmus will dissolve and give a deep blue color to the 
water. Now add a little strong vinegar, and notice the 
curious change in color : the blue turns to red. 

Ex. 153. — Into another goblet of water, colored blue 
with litmus, put a few drops of sulphuric acid : the blue 
is quickly changed to red. 

Ex. 154. — Into another solution of blue litmus put a 
few drops of nitric acid, and notice how quickly the red 
color appears. 

Ex. 155. — Take another goblet of litmus, and add 
hydrochloric acid : the blue instantly gives place to red. 

We find that there is a class of substances which are 
able to turn the color of blue litmus to red. Should you 
taste these substances you would find them all to be soar. 
They have other characters in common, but the one most 
conveniently tested is their power to turn the blue color 
of litmus to red. These substances are called acids. 

Alkalies. Ex. 156. — Take a goblet containing litmus, 
the color of which has been changed to red by an acid, 
and put into it a little ammonia. Notice that the red 
color changes back again to blue. 

Ex. 157. — Take a common glass or tin funnel, stop its 
neck by crowding some unsized paper (blotting paper) 
into it, and then pack the funnel nearly full of wood-asJtex. 
Pour some warm water upon the ashes, and as it runs 
through them and out of the stem of the funnel catch it 
in a bottle, through whose neck the funnel-stem passes 




CHEMISTRY. 75 

and upon which it rests, (Fig. 25.) When enough of 
this liquid has been caught, pour it into a goblet of litmus 
whose color has been changed to red by an acid, 
and notice that the blue color of the litmus is 
restored. (If too much acid has been added to 
the litmus it will be difficult to make it blue 
again.) 

We see in these experiments that some sub- 
stances have the power to bring back the blue 
color of litmus after it has been turned red by 
acids. Now, the most common substances of this kind 
are called alkalies. Ammonia is an alkali, so are potash 
and soda. 

Acid or Alkali ? Ex. 158, — Having a bottle and a 
cork which fits its neck, take a wire and run one end of 
it through the cork, so that when the cork is put into the 
neck of the bottle the wire will hang down some distance 
inside. Now take the cork in the hand and hold the 
other end of the wire in the fire until it is very hot. 
Plunge this hot wire into a vessel of sulphur. By this 
means considerable sulphur will cling to the wire. Now 
again hold the end of the wire in fire to inflame the 
sulphur upon it, and then plunge the burning sulphur 
into the bottle. It will continue to burn for a little while, 
filling the bottle with white fumes. These white fumes 
are quite different from either the sulphur or the air : a 
new compound has been formed by the burning sulphur. 

Remove the cork and wire and pour a little blue-litmus 
water into the bottle. Shake it well, putting the hand 
over the mouth of the bottle to keep the contents from 
escaping, and notice the change of color. Is the new 
compound an acid or an alkali ? 



76 PHYSICAL SCIENCE. 

The name of this new substance is sulphurous acid. The 
same white fumes are made when a match is lighted. 

Ex. 159. — Put some water into a goblet, and mix with 
it just enough blue litmus to give it a distinctly blue color. 
Then take a glass tube : put one end into the colored 
water, the other into the mouth, and breathe the air from 
the lungs out through it in bubbles through the water. 
After a little while notice the change in the color of the 
water : it turns to red. 

This experiment shows that an acid is contained in the 
breath as it comes from the lungs : it is called carbonic acid. 

Nitrogen and Oxygen. Ex. 160. — Prepare a bot- 
tle, with cork and wire, just as was done in Ex. 158 ; the 
bottle may be in this case a large one. Cover the end of 
the wire w T ith sulphur, and let it burn in the bottle, as in 
the other experiment. Have a second cork fitting the 
bottle : take the cork and wire out, putting the other cork 
quickly in. Cover the wire a second time with sulphur, 
and burn it in the bottle. Pepeat this until the sulphur 
quite refuses to burn in the bottle. Then turn the bottle 
cork downward : plunge its neck into a basin of water : 
take the cork out, being careful to let no air get in, and 
leave the bottle thus inverted in the water. After some 
considerable time, notice that the white fumes in the bot- 
tle are not as dense as they were. We see that the water 
is taking them out. Finally, they will all disappear. 
Notice then that the water has risen in the bottle a ways, 
and that the air (as it seems to be) above the water is 
again clear.* Now cork the bottle again, and afterward 
remove it from the water and stand it upon the table. 

* If the teacher will perform this part of the experiment beforehand, he 
need not wait for the water to take the fumes out. He can tell the pupils 



CHEMISTRY. f7 

Next take a bit of candle ; fasten it to the lower end of 
a wire (which may be bent upward for the purpose) (Fig. 
26), and having lighted it, take the cork from the 
bottle and plunge the candle in. The flame is extin- 
guished as if it had been plunged into water. If it 
were air in the bottle the candle would continue to 
burn, so that what seems to be air in the bottle is not. 

Now, this gas is what is called nitrogen. 

From this experiment several things may be 
learned : 

First. — The sulphur, burned in air, left only nitro- Fi s- 26 - 
gen : then nitrogen is a constituent of air. 

Second. — We look at the bottle and see that nitrogen is 
a gas, colorless, and transparent as air itself. 

Third. — Nitrogen extinguishes flame as quickly as 
water would. 

Fourth. — The burning sulphur took something out of 
the air of the bottle to leave the nitrogen. This some- 
thing combined with the sulphur to form the new com- 
pound — the white fumes. 

Now this substance taken out of the air by the burning 
sulphur is what is called Oxygen. So that we learn : 

Fifth. — That oxygen is another constituent of the air. 

The sulphur took the oxygen out of the air while burn- 
ing ; now, it is a fact that when any substance burns in 
air the oxygen of the air is being used up. If it were not 
for the oxygen in the air there would be no such thing as 
fire known upon the earth. 

Ex. 161. — Now light the candle and again plunge it 

that lie did the same thing with the other bottle, and that now, after stand- 
ing so long, the fumes are all gone, and then go on with the work. Always 
let the bottle which they have been using, stand, that they may see the air 
clear in it also afterward. 



Y8 PHYSICAL SCIENCE. 

into the bottle which held the nitrogen (Ex. 160), and 
which has been left, standing open, on the table. Notice 
that the flame is not quickly extinguished, as it was before. 
The nitrogen has left the bottle, we see: it must have 
gone up out of the open bottle into the air of the room. 

This experiment teaches us that nitrogen is lighter than 
air. 

Hydrogen. Ex. 162. — Put some clippings of zinc 
(sheets of zinc are used under stoves) into a wide-mouth 
bottle. Let the bottom of the bottle be more than 
covered with them, and then pour water in to more than 
cover the zinc. Next pour a little sulphuric acid into the 
bottle. In a few moments the liquid will begin to foam : 
if not, then add a little more acid, for the "boiling" 
should be violent enough to make the foaming fill the 
bottle half full. After this violent chemical action has 
gone on for a few minutes, and while still violent, bring a 
lighted match to the mouth of the bottle. An explosion 
will be heard, and a flame will at the same time appear 
at the mouth of the bottle — sometimes running down 
into it. 

We .see that a gas is produced in this experiment which 
is combustible. This combustible gas is called Hydrogen. 

Ex. 163. — "Wrap a towel around a bottle containing 
zinc and water, as in the last experiment. Pour in the 
acid as before, but touch the match to the mouth of the 
bottle very soon after the action begins. The explosion 
may be more noticeable in this experiment. 

The object of the cloth is to prevent the glass from 
flying and causing injury if, as very rarely cccurs, the 
explosion should be strong enough to break the bottle. 
Another proper caution is to tie the match to the end of 



CHEMISTRY. 79 

a wire or stick, so that the hand would be at a distance 
when the explosion occurs. 

Now notice that in this experiment the hydrogen has 
not had time to drive the air all out of the bottle, so that 
there is a mixture of air and the gas when the explosion 
occurs. 

We see that hydrogen and air form an explosive mix- 
ture. 

On this account great care should be taken, in all 
experiments with hydrogen, to expel all air from the 
apparatus before using the gas. 

Ex. 164. — Prepare a cork for the bottle in which 
hydrogen is to be made, by making a hole through the 
middle of it and inserting the end of the stem of a tobacco- 
pipe, so that when the cork is put into the neck of the 
bottle it shall fit air-tight — the pipe-stem reaching above 
it. The zinc and water being put into the bottle, add 
enough sulphuric acid, and then quickly insert 
the cork. Wait until you are sure that the air 
has been driven out by the hydrogen, and then 
bring a lighted match to the upper end of the 
pipe-stem. The hydrogen takes fire as it issues, 
and burns with a steady flame (Fig. 27). 

Notice the flame, and you will see that it gives 
a feeble light, but : 

Ex. 165. — Insert a small wire in the flame and fJHji 
you will find it quickly glowing with a red heat. 

The flame of burning hydrogen is the source of little 
light, but of very intense heat. 

Carbonic Acid. Ex. 166. — Cover the bottom of a 
glass jar (it may be a common fruit-can) with " baking 
soda," and pour upon it — a little at a time — some strong 




80 PHYSICAL SCIENCE. 

vinegar. Watch the violent boiling, or, as it is properly 
called, effervescence, which occurs. Take a bit of candle ; 
fasten it to the lower end of a wire, which is bent upward 
to support it. Light the candle and pass it down into 
the jar: the flame will be put out as it enters the gas 
given off by this chemical action. 

Notice also that the gas in the jar is colorless and 
transparent. Is it nitrogen ? We will see in another 
experiment. 

Ex. 167. — Let the jar containing the gas stand for 
some time open upon the table after the effervescence has 
stopped. Insert the lighted candle again : it is seen to be 
again extinguished, — showing that this gas is heavier 
than air, and hence is not nitrogen. 

This colorless gas, which extinguishes flame and is 
heavier than air, is called Carbonic acid. 

Ex. 168. — Take a piece of candle, an inch in length, 
and fasten it upon a cork. This may be done by dropping 
some melted tallow upon the middle of the cork and 
pressing the lower end of the candle down upon it, until 
it hardens. Light the candle, and put it into a jar, or very 
wide-mouthed bottle. Cover the jar with a plate. The 
candle standing upon the bottom of the jar goes on burn- 
ing for a little while, but begins to grow dim, and finally 
expires. Take the plate from the jar. A stiff wire which 
has been sharpened with a file may now be stuck down 
into the cork, and by this means the candle may be lifted 
out. Next pour a little lime-water* into the jar, and 
notice that on shaking it about it becomes milky. What 

* Lime-water may be prepared by taking a little slacked lime, putting it 
into a bottle, filling the bottle with water, and then shaking it thoroughly. 
Let the lime afterward settle, and then pour off the clear water above into 
another vessel for use. 



CHEMISTRY. 81 

makes this change ? Air will not do it, Nitrogen would 
not stay in the open jar, so that it cannot be nitrogen ; 
much less can it be hydrogen. The gas which was in the 
jar, to turn the lime-water milky, was colorless ; it put 
out the flame of the candle, and it was heavier than air. 
It seems to have been carbonic acid gas. As a matter of 
fact, this gas is the only one which will turn lime-water 
milky. 

But what produced this gas in the jar ? It must have 
been the burning candle. 

All common flames like this one produces carbonic' 
acid gas. 

Ex. 169. — Put a little lime-water into a goblet, and, 
taking a glass tube, or even a straw, put one end into the 
water, the other into the mouth, and breathe the breath 
out through the liquid. After a breath or two, the lime- 
water will be seen to be milky, thus showing the presence 
of carbonic acid gas. 

We learn from this experiment that carbonic acid is 
one of the things given off from the lungs in breathing. 

Ex. 170. — Breathe into a clean and dry glass jar : its 
sides are instantly covered with dew. Showing that 
water-vapor is another thing given off from the lungs in 
breathing. 

Carbonic acid and water are constantly being produced 
in the process of breathing. The first of these is made 
up of carbon and oxygen : the second of hydrogen and 
oxygen. The oxygen for both is furnished by the air 
taken into the lungs : the carbon and the hydrogen are 
furnished by waste particles or impurities of the system. 
The oxygen from the lungs enters the blood-vessels, and 
goes throughout all parts of the circulation, meeting these 
waste particles in its course. It decomposes them : com- 



82 PHYSICAL SCIENCE. 

bines with their carbon and hydrogen, and then, as car- 
bonic acid and water, goes back to the lungs, from which 
these substances are thrown out into the air. In this way 
the blood is purified.* 

Flame. Ex, 171. — Spread the wick of an alcohol 
lamp, so that, lighting it, a large flame may be obtained. 
Plunge the sulphur end of a match into the dark center 
of this flame, and notice that while the wood burns in the 
edge of the flame, the more combustible end of the match 
does not bum in the center of iU 

Ex. 172. — Take a long splinter or rod of pine wood, 
freshly smoothed, that its surface may be white, and lay 
it horizontally across the alcohol flame, just above the 
wick. When the stick begins to burn remove it, and 
notice that it is scorched in two places. The part which 
was over the center of the flame is unharmed. 

Ex. 173. — Press a piece of white paper, held horizon- 
tally, quickly down into the flame of the alcohol lamp, to 
a place just above the wick. As soon as the scorching 
begins to be seen through the paper take it quickly away. 
The paper will be burned in the shape of a ring. That 
part which was directly over the wick is unburned. 

Ex. 174. — The following experiment may be added to 
this list, provided great care is taken to follow directions : 
otherwise accident might happen. 

A common dinner-plate, when inverted, gives us a very 
shallow dish, the bottom of a plate being, as you will see, 
surrounded with a slightly elevated rim. Put a plate upon 
the table, -bottom upward, and pour alcohol into the shal- 
low dish thus obtained, being very careful that none of the 
fluid runs over upon the table or even upon the sides of 
the plate. Take a cork, about an inch in diameter : put a 



CHEMISTRY. 83 

little gunpowder upon top of it, and stand it right in the 
center of the alcohol on the plate. Take a lighted match 
and touch the alcohol at one edge of the plate y it will take 
fire : the flame will instantly spread all over the top of 
the plate, and, if no breeze waft it against the cork, the 
gunpowder will remain some time, in the center of the 
fame, unharmed ! 

These experiments clearly teach us that the interior of 
the alcohol flame is not in a state of combustion. The 
same experiments, except the last one, may be made with 
a candle-flame with much the same results. The interior 
of all ordinary flames are, like that of the alcohol-lamp, 
not burning. This ceutral part of a flame consists of 
combustible gas, and is surrounded by the burning en- 
velope. 

Ex. 175. — Eepeat Experiment 164 with apparatus 
shown in Fig. 27. Having thus obtained a hydrogen- 
flame, remember that it is being produced by the hydro- 
gen from the bottle and the oxygen in the air. Now, hold 
over this flame a clean and thoroughly dry glass jar. Its 
sides will be seen to become instantly covered with dew. 

Now, this water is the result of the action between 
hydrogen and oxygen in the flame, and hence the experi- 
ment teaches that water is made up of the two substances, 
hydrogen and oxygen. 

Ex. 176. — Now hold a clean and dry jar in the same 
way over the flame of the alcohol-lamp : its sides are soon 
dimmed with dew also. Let the same thing be done with 
a candle and with other flames. Water will be, in every 
case, deposited upon the sides of the jar. 

But, since water consists of hydrogen and oxygen, these 
results show that these two substances take part in the 



84 PHYSICAL SCIENCE. 

production of the flames. Water is a product of all 
ordinary combustion in flames : the oxygen is furnished 
from the air : the hydrogen from the body burning. 

Ex. 177. — Press the bottom of a cold dinner-plate 
down upon the flame of a candle. A moment afterward 
take the plate from the flame, and notice the black soot 
which is collected where the flame burned against it. 
There is^something beside hydrogen and oxygen, we see, 
taking part in the production of this flame. The black 
soot is carbon. The flame of a burning stick, and indeed 
almost any common flame, will furnish carbon upon a 
solid body held in it. And yet no carbon is seen when a 
flame burns freely. Why ? 

Ex. 178. — Fix a bit of candle upon a cork, by drop- 
ping a little of the melted wax or tallow upon its top and 
pressing the bottom of the candle upon it until cold. 
Light the candle and stand it on the table, and bring an 
inverted glass-jar down over it. The candle will burn 
freely for a little while, but at length it will burn more 
dimly, and finally go out. Turn the glass-jar right side 
up and pour into it a little lime-water. After shaking it 
about a little, the lime-water will become whitish, show- 
ing the presence of carbonic acid. 

Now, carbonic acid consists of oxygen and carbon, and 
it has been formed in the flame. Its oxygen has been 
furnished by the air, but its carbon must have come from 
the candle. And now we see what becomes of the carbon 
when a flames burns freely. It combines with oxygen of 
the air, and forms carbonic acid gas, which, being in- 
visible, passes unseen off into the air. 

We see from these experiments that water and car- 
bonic gas are produced by the combustion in ordinary 
flames. The hydrogen and the carbon for these are fur- 



CHEMISTRY. 85 

nislied by the fuel which burns, while the oxygen comes 
from the air. Combustion in all common instances is 
nothing but a chemical action between the oxygen of the 
air and the elements of the fuel. 



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